aptget安装ubuntudesktop失败

不知是否软件源的问题，但是已经尝试过apt-get update,不起作用。
xxxxxxx#: apt-get install ubuntu-desktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
ubuntu-desktop : Depends: doc-base but it is not going to be installed
                  Depends: eog but it is not going to be installed
                  Depends: gedit but it is not going to be installed
                  Depends: gnome-control-center but it is not going to be installed
                  Depends: gnome-media but it is not going to be installed
                  Depends: gnome-power-manager but it is not going to be installed
                  Depends: gnome-session but it is not going to be installed
                  Depends: language-selector-gnome but it is not going to be installed
                  Depends: lightdm but it is not going to be installed
                  Depends: nautilus but it is not going to be installed
                  Depends: nautilus-sendto but it is not going to be installed
                  Depends: seahorse but it is not going to be installed
                  Depends: software-center but it is not going to be installed
                  Depends: software-properties-gtk but it is not going to be installed
                  Depends: system-config-printer-gnome but it is not going to be installed
                  Depends: unity but it is not going to be installed
                  Depends: unity-2d but it is not going to be installed
                  Depends: unity-greeter but it is not going to be installed
                  Depends: update-manager but it is not going to be installed
                  Depends: update-notifier but it is not going to be installed
                  Depends: xdiagnose but it is not going to be installed
                  Depends: yelp but it is not going to be installed
                  Depends: zenity but it is not going to be installed
                  Recommends: activity-log-manager-control-center but it is not going to be installed
                  Recommends: apport-gtk but it is not going to be installed
                  Recommends: brasero but it is not going to be installed
                  Recommends: empathy but it is not going to be installed
                  Recommends: gnome-bluetooth but it is not going to be installed
                  Recommends: gnome-orca but it is not going to be installed
                  Recommends: gnome-screensaver but it is not going to be installed
                  Recommends: gnome-sudoku but it is not going to be installed
                  Recommends: gwibber but it is not going to be installed
                  Recommends: hplip but it is not going to be installed
                  Recommends: jockey-gtk but it is not going to be installed
                  Recommends: landscape-client-ui-install but it is not going to be installed
                  Recommends: nautilus-share but it is not going to be installed
                  Recommends: network-manager-gnome but it is not going to be installed
                  Recommends: onboard but it is not going to be installed
                  Recommends: plymouth-theme-ubuntu-logo but it is not going to be installed
                  Recommends: python-aptdaemon.pkcompat but it is not going to be installed
                  Recommends: rhythmbox but it is not going to be installed
                  Recommends: rhythmbox-plugin-magnatune but it is not going to be installed
                  Recommends: rhythmbox-ubuntuone but it is not going to be installed
                  Recommends: shotwell but it is not going to be installed
                  Recommends: thunderbird-gnome-support but it is not going to be installed
                  Recommends: totem but it is not going to be installed
                  Recommends: totem-mozilla but it is not going to be installed
                  Recommends: ubuntu-docs but it is not going to be installed
                  Recommends: ubuntuone-client-gnome but it is not going to be installed
                  Recommends: ubuntuone-installer but it is not going to be installed
                  Recommends: usb-creator-gtk but it is not going to be installed
                  Recommends: vino but it is not going to be installed
                  Recommends: xul-ext-ubufox but it is not going to be installed
E: Unable to correct problems, you have held broken packages.